mysql服务无法启动故障小记_mariadb server is down

问题背景：当在ubuntu中使用systemctl status mysqld.service时，输出如下（或类似）：

● mariadb.service - MariaDB database server
   Loaded: loaded (/usr/lib/systemd/system/mariadb.service; enabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Wed 2016-11-02 16:55:12 IST; 3min 6s ago
  Process: 5123 ExecStart=/usr/sbin/mysqld $MYSQLD_OPTS $_WSREP_NEW_CLUSTER $_WSREP_START_POSITION (code=exited, status=1/FAILURE)
  Process: 5070 ExecStartPre=/bin/sh -c [ ! -e /usr/bin/galera_recovery ] && VAR= ||   VAR=`/usr/bin/galera_recovery`; [ $? -eq 0 ]   && systemctl set
  Process: 5067 ExecStartPre=/bin/sh -c systemctl unset-environment _WSREP_START_POSITION (code=exited, status=0/SUCCESS)
 Main PID: 5123 (code=exited, status=1/FAILURE)
   Status: "MariaDB server is down"
 
Nov 02 16:55:11 pranav-laptop systemd[1]: Starting MariaDB database server...
Nov 02 16:55:12 pranav-laptop mysqld[5123]: 2016-11-02 16:55:12 140082509282496 [Note] /usr/sbin/mysqld (mysqld 10.1.18-MariaDB) starting as process 5
Nov 02 16:55:12 pranav-laptop mysqld[5123]: 2016-11-02 16:55:12 140082509282496 [Warning] Can't create test file /var/lib/mysql/pranav-laptop.lower-te
Nov 02 16:55:12 pranav-laptop mysqld[5123]: [90B blob data]
Nov 02 16:55:12 pranav-laptop systemd[1]: mariadb.service: Main process exited, code=exited, status=1/FAILURE
Nov 02 16:55:12 pranav-laptop systemd[1]: Failed to start MariaDB database server.
Nov 02 16:55:12 pranav-laptop systemd[1]: mariadb.service: Unit entered failed state.
Nov 02 16:55:12 pranav-laptop systemd[1]: mariadb.service: Failed with result 'exit-code'.

，可使用下面的方法先删除数据库文件（如无重要文件）：

$rm -rf /var/lib/mysql/*

删除后再重新初始化数据库目录:

 $mysql_install_db --user=mysql --basedir=/usr --datadir=/var/lib/mysql 

安装完成后会提示重启mysql服务并设置密码，详见提示。

systectl start mysqld.service

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